1. Field of the Invention
This invention relates to a novel liquid crystal compound and more particularly it relates to a liquid crystal compound having an optically active group and a chiral smectic liquid crystal composition containing the same.
2. Description of the Related Art
At present, a TN (twisted Nematic) type display mode has been most broadly employed for liquid crystal display elements. This TN liquid crystal display has a number of advantages such as low driving voltage, small power consumption, etc. However, such display elements are inferior in the aspect of the response rate to emissive type display elements such as cathode ray tube, electroluminescence, plasma display, etc. A novel TN type display element having the twist angle changed to a range of 180.degree. to 270.degree. has also been developed, but such a display element is still inferior in the aspect of the response rate. As described above, various efforts for improvement therein have been made, but any of these have not yet succeeded. However, in the case of a novel display mode using ferroelectric liquid crystals, there is a possibility of notable improvement in the response rate (Clark et al, Applied Phys. lett., 36, 899 (1980)). This mode makes use of chiral smectic phases such as chiral smectic C phase (hereinafter abbreviated to SC* phase). The phases exhibiting ferroelectric properties are not only SC* phase alone, but also it has been known that chiral smectic phases F, G, H, I, etc. also exhibit ferroelectric properties. In order to make use of such a ferroelectric liquid crystal for display elements, it has been not only required that such ferroelectric liquid crystal phases be exhibited over a broad temperature range including room temperature, but also various characteristics have been required for such elements.